Lectins are carbohydrate-binding proteins found in both plant and animal tissues. They appear to function in a variety of cell and developmental phenomena. This proposal focuses on the functional role of endogenous vertebrate lectins in early embryogenesis. An amphibian system is used because of: 1) the ease of obtaining large numbers of early embryos, which allows biochemical studies; and 2) the large size of the embryos and simple culture conditions which facilititate experimental manipulations during early development. This proposal concentrates on a soluble galactose-binding lectin found in Xenopus laevis oocytes, eggs and embryos. The bulk of this lectin is associated with yolk platelets (storage materials utilized during development) and may be released into extracellular areas to exert its functional effects, during development. The proposed work includes: 1) an investigation of the existence of multiple lectin forms; 2) attempts to follow utilization of yolk platelet lectin during development; 3) attempts to find an endogenous receptor; 4) attempts to perturb normal development in the intact embryo and in a variety of isolated cellular preparations by using univalent antibodies to the lectin, hapten inhibitors and the lectin itself; and 5) a determination of the relationship of a similar galacoside-binding lectin found in the serum of estrogen stimulated frogs to that found in X. laevis oocytes, eggs and embryos. In addition, a lectin from another amphibian species, Rana pipiens, will be investigated. This lectin requires detergents for solubilization and has an oligomannosyl specificity. Work on this lectin will concentrate on its purification as a necessary prelude to functional studies.